Modern day construction uses concrete in many forms from conventional concrete to high performance concrete. The type of concrete used will depend upon its use and the strength required. Conventional concrete has strengths in the range of 30 to 50 megaPascals (MPa). High performance concrete has strengths in the range of 200 to 400 MPa. Water usage also varies in the concretes. Conventional concrete has a water to cement material ratio (w/cm) of 0.4 to 0.6. High performance concrete has a water to cement material ratio of 0.2 to 0.3. This is because of the additives in high performance concrete. Low water to cement ratios impart high strength to the concrete.
This low water to cement material ratio leads to a concern about autogenous shrinkage. Autogenous shrinkage is internal shrinkage. A cement or concrete structure has less volume than the original water and cement material elements. As it cures it contracts. In the early curing stages of a cement or concrete structure the cement or concrete is fluid and can contract. As the cement or concrete sets up and solidifies its ability to contract diminishes. A lack of water in the internal portion of a cement or concrete structure leads to internal or autogenous shrinkage without the contraction of the entire structure. This leads to cracks and inadequate curing or strength development. As the structure solidifies there is no way to supply water to the internal portion from the outside.
There is a need to provide water to the internal portion of a cement or concrete structure to avoid internal or autogenous shrinkage.
There is also a need to provide this water while maintaining the initial consistency of the cement water mix, keeping the initial setting time within specifications and keeping the final setting time within normal limits.